Axial piston machine of swashplate design

ABSTRACT

An axial piston machine of swashplate design includes a cylindrical drum which is rotatably supported in a housing and has a plurality of cylindrical bores with pistons longitudinally displaceable therein which rest against a swashplate via a joint. The joint has a first joint part with a spherical head and a second joint part with a spherical seat for the head. The joint can be manufactured quickly and using simple, economical production engineering, in that the first joint part is rotatably held in the second joint part, which has an annular groove in the inner surface of a tubular edge, into which a wire has been introduced through a bore.

CROSS REFERENCE TO RELATED APPLICATION

The invention described and claimed hereinbelow is also described in DE 10201006908.6, filed Feb. 5, 2010. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d).

BACKGROUND OF THE INVENTION

The invention is directed to an axial piston machine of swashplate design.

Known axial piston machines of this design comprise a cylindrical drum which is rotatably supported in a housing and has a plurality of cylindrical bores with pistons longitudinally displaceable therein which rest against a swashplate via a joint, wherein a joint comprises a first joint part having a spherical head and a second joint part having a spherical seat for the head.

The general function of the joint is to ensure that a joint part rests against a running surface of the swashplate in every oblique position of the swashplate.

In the case of common joint connections, the first joint part having a spherical head is connected in a form-fit manner, after insertion, to the corresponding second joint part having a spherical seat in that an edge region of the second joint part engages behind the first joint part by way of crimping or joining, for example. Very complex production engineering is required to manufacture such a joint. The joint parts are composed of different materials. To ensure that an edge of the joint part having a spherical seat is deformed, it is usually composed of a softer material. However, to meet the high requirements regarding wear, the joint part having the spherical head is composed of harder material. Special tools are required for crimping or joining, thereby resulting in a high-cost manufacturing process.

The rear engagement of the spherical head described here enables the joint connection to be reversible.

SUMMARY OF THE INVENTION

The problem addressed by the invention is that of developing an axial piston machine of swashplate design in a manner such that the joint connection can be manufactured quickly and using simple, economical production engineering.

This problem is solved for an axial piston machine of swashplate design according to the present invention. In the case of an axial piston machine of swashplate design according to the invention, the first joint part is rotatably held in the second joint part in that the second joint part has an annular groove in the inner surface of a tubular edge, into which a wire has been introduced through a bore.

The joint connection according to the invention has a plurality of advantages.

The joint connection is considerably less expensive, because no special forming tools are required, and the material outlay required for the joint connection, and the production-engineering measures required to form an annular groove and for boring are extremely low-cost.

The joint connection according to the invention allows the joint parts to be assembled quickly and easily. The first joint part is rotatably held in the second joint part in that, once the joint parts are positioned, the wire is introduced into the annular groove of the second joint part through the bore which extends tangentially to the circumference of the annular groove.

The joint connection is disconnectable and can be easily reconnected.

According to a particularly preferred embodiment of the present invention, the first joint part is designed with a spherical head on the piston, and the second joint part having a spherical seat rests against the swashplate. Although the piston is longer in design, the spherical head is smaller.

When the first joint part rests against the swashplate and the second joint part is formed on the piston, the piston is somewhat shorter in design. The spherical head is somewhat larger and thereby brings about comprehensive hydrostatic relief.

Given that the second joint part comprises an end face facing the first joint part and the annular groove is disposed close to the end face, the annular groove is easily formed, e.g. using a turning tool, when the tubular edge is manufactured.

Given that the bore extends tangentially to the circumference of the annular groove, the wire can be easily inserted into the annular groove from the outside.

The wire is preferably a spring wire which can be inserted into the annular groove particularly easily due to its excellent bending and spring capability. Once the spring wire has been fully inserted, the spring-back property thereof causes it to engage in the annular groove and captively hold the piston head which can rotate nonetheless.

When the first joint part rests against the swashplate and has the shape of a ball, the piston is shortest in design and the sliding block design is eliminated.

When the first joint part is a sliding block that rests in a planar manner against the swashplate, the contact area between the joint and the swashplate is greater.

The sliding block is used to ensure adequate hydrostatic relief of the contact between piston and swashplate, thereby allowing high loadability of the contact. The spherical head is larger in this case and brings about comprehensive hydrostatic relief of the joint.

When the second joint part is a sliding block that rests in a planar manner against the swashplate, the contact area between the joint and the swashplate is greater.

According to this variant as well, the sliding block is used to ensure adequate hydrostatic relief of the contact between piston and swashplate, thereby allowing high loadability of the contact. In this case, the spherical head integrally formed on the piston is smaller and the joint is narrower.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of an axial piston machine of swashplate design according to the invention are depicted in the drawings. The invention will now be explained in greater detail with reference to these drawings.

FIG. 1 shows a longitudinal cross-section of a part of an axial piston machine of swashplate design according to the invention,

FIG. 2 shows a longitudinal cross-section of a joint connection having a spherical head and a spherical seat on the piston,

FIG. 3 shows a longitudinal cross-section of a joint connection having a sliding block resting squarely thereon, comprising an integrally formed spherical head and a spherical seat on the piston,

FIG. 4 shows a longitudinal cross-section of a joint connection having a sliding block resting squarely thereon, comprising a spherical seat and a spherical head on the piston,

FIG. 5 shows a longitudinal cross-section of a tubular edge of a joint connection,

FIG. 6 shows a top view of a joint connection according to FIG. 3, and

FIG. 7 shows a cross section of a joint connection through an annular groove.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The axial piston machine 1 shown in FIG. 1 comprises a driving mechanism 2 disposed in a housing 3. The main components of driving mechanism 2 are a rotatably supported drive shaft 4 having a non-rotatably connected cylindrical drum 5. Cylindrical drum 5 has cylindrical bores 6 which are disposed on a partial circle and extend in the axial direction, and in which pistons 7 are disposed in a longitudinally displaceable manner. Each piston 7, with cylindrical drum 5, limits a displacement chamber 8. The rotational motion of cylindrical drum 5 causes displacement chamber 8 to be connected via a control disk 9 to a pressure or suction connection (not depicted) in alternation.

Pistons 7, which are longitudinally displaceable in cylindrical bores 6, are preferably cylindrical. Ends of pistons 7 opposite the cylindrical drum each rest via a joint 10 against a swashplate 11. Drive shaft 4 extends through swashplate 11. This figure does not show that it is designed as a pivotably supported pivoting base having a semi-cylindrical cross section and is situated such that the particular pivot position thereof can be selected using an adjusting device 12. A running surface 13 is formed on the side thereof facing cylindrical drum 5.

When drive shaft 4 rotates, the non-rotatable connection causes cylindrical drum 5 and piston 7 to rotate as well. When swashplate 11 is swiveled, by actuating adjusting device 12, into an oblique position relative to cylindrical drum 5, pistons 7 perform reciprocating motions. In one complete rotation of cylindrical drum 5, each piston 7 completes one intake stroke and one compression stroke, thereby generating corresponding oil flows which are supplied and directed away via not-shown outlet channels, control disk 9, and not-shown pressure and suction channels.

FIGS. 2, 3 and 4 shown different designs of joints 10, via which the ends of pistons 7 opposite the cylindrical drum rest against running surface 13 of swashplate 11. Each joint 10 comprises a first joint part 20 having a spherical head 21 and a second joint part 22 having a spherical seat 23 and a tubular edge 30. First joint part 20 is held in second joint part 22 in that second joint part 22 has an annular groove 31 in the inner surface of tubular edge 30, into which a wire 40 has been introduced through a bore 32. Spherical seat 23 encompasses an upper half of spherical head 21, and a lower half of head 21 enters tubular edge 30 by about half.

Second joint part 22 having spherical seat 23 is formed on the end of piston 7 opposite the cylindrical drum, as shown in FIG. 2. The first joint part, which is rotatably supported in second joint part 22, has the shape of a ball 25. To provide hydrostatic relief of joint 10, piston 7 comprises a passage channel 26 along the central axis, which extends from displacement chamber 8 through a radially expanded opening 27 and into spherical seat 23.

Second joint part 22 having spherical seat 23 is formed on the end of piston 7 opposite the cylindrical drum, as shown in FIG. 3. First joint part 20, which is rotatably supported in second joint part 22, is a sliding block 24 which supports in a planar manner and comprises a flange-mounted, spherical head 21. A passage channel 28 is formed along the central axis of the sliding block and leads into a pressure cavity 29. To provide hydrostatic relief of joint 10, piston 7 comprises passage channel 26 along the central axis, which extends from displacement chamber 8 through opening 27 and into spherical seat 23. The sliding block surface is supplied with hydraulic oil to provide hydrostatic relief of sliding block 24 via the connection of displacement chamber 8 through passage channels 26 and 28 to pressure cavity 29.

A first joint part 20 having a spherical head 21 is formed on the end of piston 7 opposite the cylindrical drum, as shown in FIG. 4. Spherical head 21 is rotatably supported in spherical seat 23 of second joint part 22. Second joint part 22 is a sliding block 24 which supports in a planar manner and comprises a spherical seat 23. To provide hydrostatic relief of joint 10, piston 21 comprises a passage channel 26 along the central axis, which extends from displacement chamber 8 into spherical seat 23. A passage channel 28 is formed along the central axis of the sliding block, leads into a pressure cavity 29, and has a radially expanded opening 27 on the piston-head side. The sliding block surface is supplied with hydraulic oil to provide hydrostatic relief of sliding block 24 via the connection of displacement chamber 8 through passage channels 26 and 28 to pressure cavity 29.

FIG. 5 shows a section A in FIG. 2. A transition 33 having the shape of a truncated cone connects tubular edge 30 to spherical seat 23, and therefore the inner diameter of tubular edge 30 is slightly larger than spherical seat 23. Annular groove 31 is disposed on the inner surface of tubular edge 30 close to an end face 34 of the edge. Tubular edge 30 ends with a groove flank 35 of annular groove 31, which is rounded off toward end face 34 and is slightly shorter.

FIG. 6 shows the top view of the joint connection according to FIG. 3, in which second joint part 22 having spherical seat 23 is formed on the end of piston 7 facing away from the cylindrical drum, and first joint part 20, which is rotatably supported in second joint part 22, is designed as sliding block 24 which supports in a planar manner and comprises a flange-mounted, spherical head 21. Bore 32 is disposed close to end face 34 of tubular edge 30.

FIG. 7 shows the cross section of the joint connection through bore 32 which extends tangentially into annular groove 31. The inner diameter of bore 32 corresponds to the width of annular groove 31 in FIG. 7. Wire 40 captively holds spherical head 21 in spherical seat 23. The length of wire 40 is slightly shorter than the circumference of annular groove 31, and therefore wire 40 extends along entire annular groove 31, to ensure uniform loading of wire 40.

The joint is assembled in a particularly simple manner: first joint part 20 is positioned in second joint part 22 and then wire 40, e.g. a spring wire, is inserted or injected through bore 32 into annular groove 31. The cross section of wire 40 is matched to the cross section of annular groove 31. Wire 40 is introduced tangentially into the annular groove. Once wire 40 has been fully inserted, the spring-back property thereof causes it to engage in annular groove 31 and captively hold spherical head 21 which can rotate nonetheless.

Running surface 13 can also be designed as a separate part, as shown in FIGS. 2, 3 and 4 in particular. In the sliding block design, a separate running surface is typically not provided; the sliding blocks run directly on the swashplate surface.

According to a variant spherical piston, it can be advantageous in terms of cost and function to integrate a separate running surface since this makes it possible to use standard bearing parts, among other things.

The diameter of bore 32 in tubular edge 30 need not necessarily correspond to the width of annular groove 31. However, it must be larger than the diameter of wire 40.

The tangential extension of bore 32 is not mandatory, but it simplifies the introduction of wire 40. Bore 32 can also be offset slightly inwardly in terms of the outer diameter of annular groove 31, thereby preventing wire 40 from slipping out.

Transition 33 preferably has the shape of a truncated cone since this is easy to realize in terms of production engineering. The transition may also have a seamless design or project radially.

Wire 40 is preferably an elongated, rod-shaped spring element which extends as a straight line in the relaxed state. This design is not mandatory, however. Wire 40 may also be an annular spring element. However, in every case it must bear outwardly in the installed state, or it is necessary for the installation space for wire 40 having lateral introduction to be designed such that wire 40 cannot slip forward, thereby ensuring that spherical head 21 is captively held.

Due to the lateral introduction of wire 40, the sliding block design has the additional advantage that the play between piston 7 and sliding block 24 can be kept lower than it is when introduction occurs from the front.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an axial piston machine with a swashplate design, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 

1. An axial piston machine (1), comprising: a housing (3); a cylindrical drum (5) rotatably supported in the housing (3) and having a plurality of cylindrical bores (6) with pistons (7) longitudinally displaceable therein; a swashplate (11), wherein said piston (7) rest against the swashplate (110 via a joint (10), wherein the joint (10) comprises a first joint part (20) having a spherical head (21) and a second joint part (22) having a spherical seat (23) adapted to receive the head (21), wherein the first joint part (20) is rotatably held in the second joint part (22) in that the second joint part (22) has an annular groove (31) in the inner surface of a tubular edge (30), into which a wire (40) has been introduced through a bore (32).
 2. The axial piston machine (1) according to claim 1, wherein the first joint part (20) is formed on the piston (7) and the second joint part (22) rests against the swashplate (11).
 3. The axial piston machine (1) according to claim 1, wherein the first joint part (20) rests against the swashplate (11) and the second joint part (22) is formed on the piston (7).
 4. The axial piston machine (1) according to claim 1, wherein the second joint part (22) has an end face (34) that faces the first joint part (20) and the annular groove (31) is disposed close to the end face (34).
 5. The axial piston machine (1) according to claim 1, wherein the bore (32) extends tangentially to the circumference of the annular groove (31) and leads into the annular groove (31).
 6. The axial piston machine (1) according to claim 1, wherein the wire (40) is a spring wire.
 7. The axial piston machine (1) according to claim 1, wherein the first joint part (20) rests against the swashplate (11) and has the shape of a ball (25).
 8. The axial piston machine (1) according to claim 1, wherein the first joint part (20) is a sliding block (24) which rests in a planar manner against the swashplate (11).
 9. The axial piston machine (1) according to claim 1, wherein the second joint part (20) is a sliding block (24) which rests in a planar manner against the swashplate (11). 